How to preoperatively evaluate a patient with impaired renal function (eGFR 45) before surgery?

Preoperative Evaluation of a Patient with eGFR 45

For a patient with eGFR 45 mL/min/1.73 m² undergoing surgery, obtain baseline electrolytes, creatinine, complete blood count, and ECG, while ensuring nephrotoxic medications are adjusted or discontinued and adequate renal perfusion is maintained perioperatively. 1, 2

Risk Stratification and Baseline Assessment

Patients with eGFR 45 mL/min/1.73 m² fall into the moderate renal impairment category (CKD Stage 3a-3b) and require comprehensive preoperative evaluation to minimize perioperative acute kidney injury and optimize outcomes. 3, 1

Essential Laboratory Testing

• Measure serum creatinine and electrolytes to establish baseline renal function and identify electrolyte abnormalities that may complicate anesthesia or surgery 1
• Obtain complete blood count as patients with eGFR <60 mL/min/1.73 m² have increased risk of anemia, which occurs in >50% of patients with eGFR <30 mL/min/1.73 m² 3, 1
• Check serum calcium, phosphate, PTH, and alkaline phosphatase at least once in patients with eGFR <45 mL/min/1.73 m² to assess for metabolic bone disease 3
• Perform ECG for patients with renal impairment undergoing intermediate or high-risk surgery, as this population has increased cardiovascular risk 1

Medication Management

Review and adjust all medications based on renal function to prevent drug accumulation and toxicity: 2, 4

• Discontinue or hold metformin if the patient is taking it, as initiation is not recommended with eGFR 30-45 mL/min/1.73 m², and existing therapy requires benefit-risk assessment 4
• Stop metformin at the time of surgery due to risk of volume depletion, hypotension, and lactic acidosis when food and fluid intake is restricted 4
• Avoid or use NSAIDs with extreme caution due to nephrotoxic effects that can precipitate acute kidney injury 2
• Adjust dosages of renally-excreted medications according to eGFR to prevent acute kidney injury 2
• Review diuretics, ACE inhibitors, ARBs, and digoxin as these predispose to electrolyte abnormalities requiring monitoring 1

Cardiovascular and Functional Assessment

• Assess functional capacity to determine if the patient can achieve ≥4 METs or climb ≥2 flights of stairs, which generally allows proceeding to surgery without extensive cardiac testing 1
• Identify active cardiac conditions including unstable coronary syndromes, decompensated heart failure, significant arrhythmias, or severe valvular disease that require evaluation before surgery 1
• Recognize that renal impairment is an independent risk factor for perioperative complications and may indicate underlying cardiovascular disease 1

Intraoperative Planning

Communicate specific renal protection strategies to the anesthesia and surgical teams: 2

• Maintain mean arterial pressure between 60-70 mmHg (or >70 mmHg if hypertensive) to ensure adequate renal perfusion pressure 2
• Implement goal-directed fluid therapy to optimize renal perfusion while avoiding both hypovolemia and fluid overload 2
• Avoid nephrotoxic agents including aminoglycosides, contrast media (unless absolutely necessary), and NSAIDs 2
• Plan for close monitoring of urine output and hemodynamic parameters throughout the procedure 2

Contrast Media Considerations

If contrast imaging is required perioperatively: 4

• Hold metformin (if applicable) at the time of or prior to iodinated contrast procedures in patients with eGFR 30-60 mL/min/1.73 m² 4
• Re-evaluate eGFR 48 hours after contrast exposure before restarting metformin, ensuring renal function remains stable 4
• Ensure adequate hydration before and after contrast administration to minimize risk of contrast-induced nephropathy 2

Postoperative Monitoring

Establish a plan for enhanced postoperative surveillance: 2

• Monitor urine output and serum creatinine closely in the immediate postoperative period to detect acute kidney injury early 2
• Maintain adequate hydration while avoiding fluid overload, particularly in patients with cardiac comorbidities 2
• Continue avoiding nephrotoxic medications including NSAIDs for postoperative pain management 2
• Implement early mobilization and enteral feeding as part of enhanced recovery protocols 2

Special Surgical Considerations

The type and invasiveness of surgery influences risk stratification: 1, 5

• Low-risk procedures (cataract surgery, minor dermatologic procedures) may proceed with minimal additional testing beyond baseline assessment 1
• Intermediate and high-risk procedures require more comprehensive evaluation including ECG and consideration of cardiac risk factors 1
• Urologic procedures or implantation of foreign material (prosthetic joints, heart valves) warrant urinalysis despite the general recommendation against routine urinalysis 1

Common Pitfalls to Avoid

• Do not routinely order chest radiography unless the patient has new or unstable cardiopulmonary symptoms, as it is not indicated for asymptomatic patients 1
• Do not perform coagulation studies unless there is a history of bleeding disorders, liver disease, or anticoagulant use 1
• Do not continue metformin through the perioperative period without careful consideration of volume status and surgical risk 4
• Do not assume eGFR accurately reflects true GFR in all patients; consider that eGFR equations have limitations and measured GFR may be needed for critical decisions 6, 7